vco

Voltage-controlled oscillator

Syntax

y = vco(x,fc,fs)

y = vco(x,[Fmin Fmax],fs)

Description

y = vco(x,fc,fs) creates a signal that oscillates at a frequency determined by the real input vector or matrix x with sampling frequency fs. If x is a matrix, vco produces a matrix whose columns oscillate according to the columns of x.

example

y = vco(x,[Fmin Fmax],fs) scales the frequency modulation range so that ±1 values of x yield oscillations of Fmin Hz and Fmax Hz, respectively.

example

Examples

collapse all

Spectrogram of Chirp Signal

Open Live Script

Generate two seconds of a signal composed of a voltage-controlled oscillator (VCO) and four Gaussian atoms. The instantaneous frequency is modulated by a chirp function. The sample rate is 14 kHz.

fs = 14000;
t = (0:1/fs:2)';

gaussFun = @(A,x,mu,f) exp(-(x-mu).^2/(2*0.01^2)).*sin(2*pi*f.*x)*A';
s = gaussFun([1 1 1 1],t,[0.2 0.5 1 1.75],[10 60 25 5]*100)/10;
x = vco(chirp(t+.1,0,t(end),3).*exp(-2*(t-1).^2),0.2*fs,fs);

s = s/10+x;

Plot the spectrogram of the generated signal. Specify 90% overlap and moderate spectral leakage.

pspectrum(s,fs,"spectrogram",OverlapPercent=90,Leakage=0.5)

Figure contains an axes object. The axes object with title Fres = 164.0842 Hz, Tres = 15.6429 ms, xlabel Time (s), ylabel Frequency (kHz) contains an object of type image.

Spectrogram of Sawtooth Signal

Open Live Script

Generate two seconds of a signal sampled at 10 kHz whose instantaneous frequency is a triangle function of time.

fs = 10000;
t = 0:1/fs:2;
x = vco(sawtooth(2*pi*t,0.75),[0.1 0.4]*fs,fs);

Plot the spectrogram of the generated signal. Specify the leakage as 0.80 and the overlap between adjoining segments as 95%.

pspectrum(x,fs,'spectrogram','Leakage',0.80,'OverlapPercent',95)

Figure contains an axes object. The axes object with title Fres = 106.1965 Hz, Tres = 15.7 ms, xlabel Time (s), ylabel Frequency (kHz) contains an object of type image.

Input Arguments

collapse all

`x` — Input data
real vector | real matrix

Input data, specified as a real vector or real matrix. x ranges from –1 to 1, where x = –1 corresponds to 0 frequency output, x = 0 corresponds to fc, and x = 1 corresponds to 2*fc.

`fc` — Carrier frequency
`fs`/`4` (default) | real positive scalar

Carrier or reference frequency used to modulate the input signal, specified as a real positive scalar.

`Fmin`, `Fmax` — Frequency modulation range limits
real vector

Frequency modulation range limits, specified as a real vector. For best results, Fmin and Fmax should be in the range 0 to fs/2.

Note

vco performs FM modulation using the modulate function.

`fs` — Sample rate
positive scalar

Sample rate, specified as a positive scalar. The sample rate is the number of samples per unit time. If the unit of time is seconds, then the sample rate has units of Hz.